Author(s): HU, X., HASEGAWA, H., Institution: UNIVERSITY OF HIROSHIMA, Country: JAPAN, Abstract-ID: 1985

INTRODUCTION:
Exercise in hot environments induces marked hyperthermia and elevates peripheral skin blood flow to facilitate heat dissipation, which may redistribute circulating blood volume and compromise cerebral perfusion, particularly in the middle cerebral artery (MCA) territory. Such cerebrovascular constraints are thought to impair higher-order cognitive functions, including attention and executive function. Although targeted cooling of the hands and feet, which contain dense arteriovenous anastomoses (AVAs), has been shown to effectively attenuate thermal strain, its influence on cerebral blood flow and cognitive function during recovery from exercise-induced hyperthermia remains largely unexplored. Therefore, this study investigated whether targeted hand and foot cooling preserves MCA blood flow velocity (MCAv) and facilitates cognitive recovery following exercise in the heat.
METHODS:
Eleven healthy collegiate athletes completed a randomized crossover experiment under hot environmental conditions (Ta: 35°C, RH: 50%). Participants performed 40 min of constant-load cycling at 52% of VO2peak, followed by one of two recovery conditions: (1) CON, involving seated rest without cooling, or (2) COOL, in which the hands and feet were immersed to the level of the wrist and ankle in circulating cold water (15–18°C) for 15 min. Thermoregulatory and cardiovascular variables, including rectal temperature (Tre), mean skin temperature (Tsk), forehead deep temperature (DFT), and heart rate (HR), were assessed throughout the protocol. Beat-to-beat R–R intervals were continuously recorded, and time- and frequency-domain heart rate variability indices were derived to evaluate autonomic nervous system activity. MCAv was continuously measured using transcranial Doppler ultrasound with a fixed probe over the temporal window. Cognitive function was assessed before exercise, immediately post-exercise, and following the intervention using validated CogniFit tasks that focused on attention and executive function.
RESULTS:
Tre, Tsk, and DFT were significantly lower in the COOL condition than in the CON condition throughout the recovery period (all p < 0.05). HR was also significantly reduced during COOL (p < 0.05). MCAv was significantly higher in the COOL condition from 5 min after the onset of cooling and remained elevated throughout the intervention period (p < 0.05). Parasympathetic nervous system activity was enhanced during COOL, as evidenced by a significantly greater high-frequency component of HR variability (p < 0.05). Although cognitive reaction time did not differ between conditions, cognitive accuracy during recovery was significantly greater in the COOL condition compared with CON (p < 0.05).
CONCLUSION:
This study provides novel evidence that targeted cooling of the hands and feet during recovery from exercise-induced hyperthermia reduces central thermal strain, preserves middle cerebral artery blood flow velocity, enhances parasympathetic activity, and improves cognitive accuracy.